Process and device for converting a liquid stream flow into a gas stream flow

ABSTRACT

In a method and an apparatus for converting a liquid flow into a gas flow, a liquid flow is introduced into an evaporation volume, the liquid flow is dispersed so as to enlarge the surface of the liquid, the dispersion being not caused by a change of pressure and taking place without admixture of a medium, and the evaporated liquid flow is conducted out of the evaporation volume.

This application is the National Stage of International Application No.PCT/EP95/04846 filed on Dec. 8, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention refers to a method and an apparatus for convertinga liquid flow into a gas flow and especially to a method and anapparatus for converting a liquid flow into a gas flow by means ofdispersion.

2. Description of the Related Art

Various methods of converting a liquid flow into a gas flow are known.They are used e.g. in cases where liquid chemicals must be convertedinto the gaseous phase, e.g. when specific chemical deposition processesare carried out in the field of semiconductor technology.

The best known method for converting a liquid flow into the gaseousphase is the so-called bubbler method. This method comprises the stepsof heating the liquid to be evaporated to a predetermined temperatureand introducing a so-called carrier gas, e.g. nitrogen or oxygen,continuously below the surface of the liquid to be evaporated. Thecarrier gas bubbles rise in the liquid and are saturated with the vapourof the liquid. A mixture of vapour and carrier gas forms in a closedvolume above the surface of the liquid, the mixture being dischargede.g. into a reactor connected to the volume and being then used in theabove-mentioned chemical deposition processes. When an adequately lowcounterpressure (e.g. reactor pressure) and a high vapour pressure ofthe liquid are used, a vapour stream can also be produced without acarrier gas. Depending on the vapour pressure of the liquid, this,however, requires high temperatures of the liquid.

Although the bubbler method described hereinbefore is simple with regardto the apparatus used, the control of the vapour stream is verydifficult. The mass flux of the vapour/gas mixture is determined by thetemperature of the liquid, the pressure above the surface of the liquidand the carrier gas flow rate. In addition, the temperature of thecarrier gas and the height of the column of liquid can influence thestability and the continuity of the vapour stream. In the case of thisknown method, major variations of the mass flux and even a completeinterruption of the mass flux caused by gas cavities may occur. Ingeneral, it is not always avantageous to admix a carrier gas fortechnological reasons.

Another method is based on the principle of achieving an evaporationprocess which is referred to as flash evaporation. Flash evaporationprocesses are normally used for evaporating materials with differentvapour pressures. The desired composition of the gas mixture is achievedin that small amounts of the starting material, in a definedcomposition, are evaporated completely. In this connection, adistinction is made between the introduction of the material, the methodof distributing the material to be evaporated and the heating.

An essential drawback of this method is that it is complicated anddifficult to achieve a uniform distribution of the liquid in theevaporator. In the flash evaporation method, the liquid is introduced inthe evaporator by means of a mass flow controller or a dosing pump. Themass flow controller supplies liquid under a very low pressure, acircumstance which makes it more difficult to distribute the liquiduniformly over the evaporator surface which is a large surface in mostcases. This may give rise to temperature inhomogeneities caused bydifferent cooling processes, and these temperature inhomogeneitiesresult in local condensation. The dosing pump is capable of producing ahigh pressure, but, if the liquid contains gas cavities, this will havethe effect that the liquid flow is disturbed or interrupted completely.

A further method, which is disclosed in the European patent applicationEP-A-0559259, is based on the principle that a liquid to be evaporatedis introduced in a mixing chamber and that a carrier gas flow issimultaneously introduced in the mixing chamber in close proximity tothe liquid inlet nozzle. The carrier gas flow is introduced under apressure which is so high that a liquid/gas mixture is already generatedimmediately behind the liquid inlet nozzle, the liquid/gas mixture beingintroduced in an evaporator chamber. This evaporator chamber can haveheat supplied thereto so that the liquid will evaporate and a gasmixture will form which is finally discharged from the evaporatorchamber.

Other known methods are based on the principle that a liquid to beevaporated is applied to a large, heated surface so as to achieve a goodheat transfer and rapid evaporation.

The publication Applied Physics Letters, Vol. 56, No. 25, pages 2522 and2523 describes a method of spraying in the interior of a pyrolysisreactor. A liquid is supplied to an ultrasonic nozzle by means of whichthe liquid is atomized. The atomized liquid is entrained by a stream ofoxygen.

Patent Abstracts of Japan, Vol. 14, No. 77 corresponding to JP 1294525concerns the spraying of a solution with metal components making use ofan ultrasonic spray means. From this publication it can not be inferredwhether the spraying of the liquid takes place here with or without achange of pressure or whether it is carried out with or withoutadmixture of a medium.

Patent Abstracts of Japan, Vol. 6, No. 90 corresponding to JP-A-57022136concerns the production of optical glass fibres. A glass-forming rawmaterial liquid is introduced in a reservoir and atomized by means of avibration energy provided by an ultrasonic vibrator, an inert gasintroduced in the reservoir conveying the material to an outlet.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a method and anapparatus for converting a liquid flow into a gas flow in the case ofwhich control of the vapour stream formed is simple, a uniformdistribution of the liquid in the evaporator is obtained, completeevaporation of the liquid is guaranteed, and disturbances orinterruptions of the liquid flow are prevented.

The invention is a method of converting a liquid flow into a gas flow.The liquid flow is introduced into an evaporation volume and heat issupplied to the evaporation volume. The liquid flow is dispersed so asto enlarge the surface of the liquid, the dispersion being not caused bychange of pressure, but by subjecting the liquid to a mechanicalvibration, and taking place without any admixture of a medium. Theevaporated liquid flow is conducted out of the evaporation volume.

The invention is an apparatus for converting a liquid flow into a gasflow. The apparatus includes an inlet means for the liquid flow, adispersing element for dispersing the liquid flow by subjecting it to amechanical vibration, the dispersion being not caused by a change ofpressure and taking place without any admixture of a medium, a heatingdevice by means of which an evaporation volume can be heated to atemperature depending on the liquid to be evaporated so that thedispersed liquid evaporates completely, and a discharge means.

One advantage of the present invention is that a liquid flow isconverted into a gas flow in such a way that it is guaranteed that, whenthe liquid has been introduced, the surface of the liquid is enlarged,whereby a quick and complete evaporation is achieved subsequently sothat a stable, continuous vapour/gas flow is generated.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the apparatus according to the presentinvention which is used for carrying out the method according to thepresent invention is described in detail on the basis of the figureenclosed, in which:

FIG. 1 shows an apparatus for converting a liquid flow into a gas flow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Prior to describing the apparatus according to the present invention,which is used for converting a liquid flow into a gas flow, the methodaccording to the present invention will be described hereinbelow.

In a first step, a liquid flow to be evaporated is introduced through anopening into a so-called evaporation volume. In this evaporation volume,the evaporation takes place subsequently.

In a next step, the liquid flow is dispersed, whereby the surface of theliquid is enlarged substantially. This dispersion is not caused by achange of pressure and takes place without admixing a medium. Thedispersion takes therefore place with such efficiency that essentiallyno non-dispersed amount of liquid forms in the evaporation volume. Dueto the dispersion of the liquid, the liquid evaporates quickly so thatthe formation of a non-dispersed amount of liquid is essentiallyprevented in the evaporation volume.

In a subsequent step, the evaporated liquid flow is conducted out of theevaporation volume.

For the method according to the present invention it is of essentialimportance that, when the liquid is being supplied, the dispersion andthe evaporation take place completely and without any delay. Thisguarantees that the whole amount of liquid supplied is dispersed withina sufficiently short period of time, the dispersion guaranteeing thatthe evaporation takes place quickly.

In accordance with a preferred embodiment of the present invention,dispersion is caused by subjecting the liquid to a mechanical vibration.These mechanical vibrations can be generated e.g. by an ultrasonictransducer so that the dispersion is caused by ultrasonic waves.

In accordance with a further preferred embodiment of the presentinvention, the evaporated liquid flow has admixed thereto one or severalcarrier gases and/or process gases when it has left the evaporationvolume and the resultant vapour/gas flow is discharged via an outlet.

Depending on the liquid to be evaporated, the evaporation volume can beheated to a predetermined temperature. Thermal energy is in this casesupplied so quickly that no non-dispersed liquid phase forms in theevaporation volume, i.e. that a complete evaporation of the liquid flowis guaranteed.

In accordance with a further embodiment, the method according to thepresent invention includes a step by means of which non-evaporatedamounts of liquid are held back so that it can be excluded thatnon-evaporated amounts of liquid reach the outlet or the outlets.

In the following, an apparatus for converting a liquid flow into a gasflow will be described in detail on the basis of FIG. 1.

An inlet means 100 is used for introducing a liquid to be evaporatedinto an evaporation volume 102. This evaporation volume 102 is a cavityarranged in an evaporation body 104.

A dispersing element 106 is arranged on said evaporation volume 102 insuch a way that it covers said evaporation volume 102.

The dispersing element 106 disperses the liquid flow by subjecting it toa mechanical vibration, the dispersion being not caused by a change ofpressure and taking place without admixture of a medium.

The apparatus according to the present invention is also provided with adischarge means 108.

In the preferred embodiment shown in FIG. 1, the dispersing element 106includes an ultrasonic transducer so that the dispersion is caused byultrasonic waves.

After having passed the inlet, the dispersed liquid 110 is contained inthe evaporation volume 102 where it evaporates completely, i.e. it isconverted into a gas flow 112.

The discharge means 108 of the embodiment according to the presentinvention shown in FIG. 1 includes an admixing device 114 by means ofwhich one or several carrier gases can be admixed to the evaporatedliquid flow so that a vapour/gas flow 116 is obtained, which leaves theapparatus according to the present invention via an outlet 118. Thegases referred to as carrier gases hereinbelow with regard to thepresent invention can also participate in the process in question. Suchgases are then normally referred to as process gases.

In order to prevent a discharge of non-evaporated liquid, the dischargemeans 108 additionally includes a device 120 which prevents preciselysuch discharge of non-evaporated liquid.

According to a further embodiment of the apparatus according to thepresent invention, which is not shown, said apparatus can additionallyinclude a heating means with the aid of which the evaporation volume 102can be heated to a temperature depending on the liquid to be evaporatedso that a complete evaporation of the dispersed liquid 110 into a gasflow 112 will take place.

It is apparent that the present invention is not limited to an apparatuswith one out outlet, but that said apparatus can, of course, be providedwith one or with a plurality of outlets by means of which the resultantvapour/gas flow can be removed.

What is claimed is:
 1. A method of converting a liquid flow into a gasflow in a heated evaporation cavity, comprising the following methodsteps:supplying the liquid flow towards said evaporation cavity;dispersing the liquid flow by means of ultrasonic waves so as to enlargethe surface of the liquid, said dispersion being not caused by change ofpressure, but by subjecting the liquid to a mechanical vibration, andtaking place without any admixture of a medium; introducing saiddispersed liquid into said evaporation cavity; evaporating saiddispersed liquid to generate a gas flow; conducting the gas flow out ofthe evaporation cavity; admixing one or several carrier gases and/orprocess gases to the gas flow when said gas flow has left theevaporation cavity; conducting the resultant gas flow out of theapparatus via an outlet; and holding back non-evaporated liquid so thatno non-evaporated liquid will be discharged.
 2. The method according toclaim 1, further comprising the following method step:heating theevaporation cavity to a temperature depending on the liquid to beevaporated, in such a way that the dispersed liquid evaporatescompletely.
 3. An apparatus for converting a liquid flow into a gasflow, comprising:an inlet means for the liquid flow; a dispersingelement for dispersing the liquid flow by subjecting it to a mechanicalvibration, said dispersion being not caused by a change of pressure andtaking place without any admixture of a medium; an evaporation cavityreceiving said dispersed liquid; a heating device by means of which saidevaporation cavity can be heated to a temperature depending on theliquid to be evaporated so that the dispersed liquid evaporatescompletely; and a discharge means; wherein the discharge means isprovided with an admixing device admixing to the evaporated liquid flowone or more carrier gases and/or process gases; wherein the dischargemeans is provided with a device which prevents an escape ofnon-evaporated liquid; and wherein the dispersing element is providedwith an ultrasonic transducer.